Integrated circuits may be formed using various photolithographic techniques. Such techniques involve exposing a photoresist layer to a light source through a patterned photo-mask. As the patterns formed into photoresist layers become increasingly dense, it becomes difficult to use a single photo-mask to form a pattern in the photoresist layer because features within the nanometer range are smaller than the resolution of a light source to which the photo-resist layer is exposed. Thus, multiple masks may be used to form the features within a pattern.
In some cases, a target pattern is formed through use of both a main pattern and a cut pattern. The cut pattern removes features formed by the main pattern in order to achieve the desired target pattern. Cut patterns can be used to split main patterns into smaller features to create the desired patterns. Using such techniques provides certain advantages to the photolithographic process. For example, it is desirable to have a large process window. The process window refers to the range of focus and exposure settings that will still produce the desired features into the photo-resist layer. A process window can be improved by having features within a pattern adhere to a uniform density. This may involve placement of “dummy” features. Dummy features are extra features that are placed within the main pattern in order to maintain feature density, but do not serve any function within the circuit for which the pattern is designed. Cut features can also be used to separate dummy features from real functional features.
Placement of the cut features within the cut feature mask is an important consideration. If two cut features are too close to each other, then it can be difficult to form the cut features properly. Moreover, the cut features may adversely affect adjacent features. Thus, it is beneficial to consider the placement of cut features when designing a layout for a target pattern.